High performance micro-rib tube

ABSTRACT

A heat transfer tube utilized in a condenser or an evaporator of a heat exchanger includes a plurality cavities to increase heat transfer. A plurality of substantially trapezoidal shaped substantially parallel ribs are formed by a first roll embossing step. A second roll embossing step is repeated at a different helix angle to slightly deform the ribs, creating a plurality of substantially parallel microgrooves and a cavity on the interior end of each microgroove. The cavities are substantially branched or substantially V-shaped and increase heat transfer.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to a method of enhancing the performance of a heat transfer tube.

[0002] Heat transfer tubes are utilized in heat exchangers as either vaporization or condensation tubes. A plurality of grooves are commonly rolled on the interior surface of the heat transfer tube by a roll forming process, increasing the surface area for two-phase heat transfer. By increasing the surface area, the amount of surface exposed to fluid is increased, promoting turbulence. Heat transfer tubes are made of metal, such as copper or copper alloy.

[0003] When heat transfer tubes are utilized in condensers, the grooves in the tubes increase the turbulence of the vapors and help to retain the fluid.

[0004] When heat transfer tubes are utilized in evaporators, the grooves provide more nucleation sites, promoting nucleate boiling of the fluid. The surface tension distributes the vaporizing liquid evenly, promoting efficient film evaporation. This increases the efficiency of conversion of liquid to vapor.

[0005] Hence, there is a need in the art for a method of enhancing the performance of a heat transfer tube.

SUMMARY OF THE INVENTION

[0006] The present invention relates to a method of enhancing the performance of a heat transfer tube.

[0007] A heat transfer tube utilized in a condenser or an evaporator of a heat exchanger includes a plurality of substantially parallel ribs and a plurality of substantially parallel microgrooves.

[0008] A plurality of substantially parallel ribs substantially trapezoidal in shape and are formed by a first roll embossing step. The ratio of the rib height to the interior diameter of the heat transfer tube is between 0.01 to 0.05. The width of the ribs at the rib base is between 0.005 to 0.01 of an inch and the rib apex angle is between 0 and 60°. Approximately 20 to 200 ribs per inch are formed on the interior tube circumference of the heat transfer tube.

[0009] A second roll embossing step is performed a different helix angle to substantially deform the plurality of ribs. The second roll embossing step is rolled at a helix angle between 0 and 45° from the longitudinal axis of the tube. The ratio of the rib height to the interior diameter is between 0.01 to 0.05. The width of the ribs at the rib base is between 0.005 to 0.01 of an inch. Additionally, the rib apex angle is between 0 and 60°. After deforming the ribs, there are approximately 20 to 100 ribs per inch formed on the interior tube circumference of the heat transfer tube. The second roll embossing step deforms the ribs to create a plurality of microgrooves and produces a cavity on the interior end of each microgroove.

[0010] The cavities promote nucleate boiling, flow induced turbulence, and improve both evaporating and condensing heat exchanger performance. The cavities are substantially branched or substantially V-shaped. The nominal cavity depth is less than 75% of the height of the ribs, and the nominal cavity openings are less than 0.005 of an inch wide.

[0011] Accordingly, the present invention provides a method of enhancing the performance of a heat transfer tube.

[0012] These and other features of the present invention will be best understood from the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

[0014]FIG. 1 illustrates a heat transfer tube of a heat exchanger.

[0015]FIG. 2 illustrates the plurality of ribs formed by the first roll embossing step.

[0016]FIG. 3 illustrates the helix angle formed by the first roll embossing step and the second roll embossing step.

[0017]FIG. 4 illustrates the deformed ribs, microgrooves, and cavities formed by the second roll embossing step.

[0018] FIGS. 5 illustrates a cross sectional view of a cavity of the preferred embodiment.

[0019]FIG. 6 illustrates a cross-sectional view of a cavity of a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020]FIG. 1 schematically illustrates a heat transfer tube 10 utilized in a heat exchanger 11, typically a condenser or an evaporator. In the preferred embodiment, the heat transfer tube 10 is made of copper or a copper alloy. The heat transfer tube 10 includes an interior surface 12, a plurality of substantially parallel ribs 14, a plurality of substantially parallel microgrooves 16, a plurality of cavities 24, and an interior diameter D.

[0021] As shown in FIG. 2, the plurality of substantially parallel ribs 14 formed by a first roll embossing step are substantially trapezoidal in shape. Each rib 14 has a rib base 18, a pair of opposing sides 20 a and 20 b, and a rib top 22. Each of the ribs further has a rib height h₁ measured from the interior diameter D to the rib top 22. In the preferred embodiment, the ratio of the rib height h₁ to the interior diameter D (h_(1/)D) is between 0.01 and 0.05. The width w₁ of the ribs at the rib base 18 is between 0.005 and 0.01 of an inch and the rib apex angle β₁ is between 0 and 60°. In the preferred embodiment, the rib apex angle β₁ is less than 25°. The rib apex angle β₁ is the angle created by the opposing sides 20 a and 20 b. There are approximately 20 to 200 ribs 14 per inch of the interior tube circumference C of the heat transfer tube 10.

[0022] As shown in FIG. 3, the plurality of substantially parallel microgrooves 16 are formed by deforming the plurality of ribs 14 by a second roll embossing step repeated at a different helix angle α. The helix angle α is between 0 and 45° from the longitudinal axis of the tube 10.

[0023] After the second roll embossing step, the ribs 14 are slightly deformed, as shown in FIG. 4. The ratio of the rib height h₂ to the interior diameter D (h_(2/)D) is between 0.01 and 0.05. In the preferred embodiment, the ratio of the rib height h₂ to the interior diameter D (h_(2/)D) is between 0.015 and 0.03. The width w₂ of the ribs 14 at the rib base 18 is between 0.005 and 0.01 of an inch, and the rib apex angle β₂ is between 0 and 60°. After rolling, there are approximately 20 to 100 ribs 14 per inch of the interior tube circumference C of the heat transfer tube 10. By deforming the plurality of ribs 14, a plurality of microgrooves 16 are produced and a cavity 24 is created on the interior end of each microgroove 16.

[0024] The cavities 24, if properly configured, can promote nucleate boiling, flow induced turbulence, and improve both evaporating and condensing heat exchanger performance. As illustrated in FIGS. 5 and 6, the cavities 24 are substantially branched or substantially V-shaped, respectively. The nominal cavity depth δ₁ and δ₂, respectively, is less than 75% of the height h₂. In the preferred embodiment, the nominal cavity depth δ₁ and δ₂, respectively, is less than 40% of the height h₂. The nominal cavity opening δ₁ and δ₂, respectively, is less than 0.005 of an inch. The preferred shape of the cross section of the microgrooves 16 is shown in FIGS. 5 and 6.

[0025] The plurality of cavities 24 are created by a two-step process. In the first step, a flat copper strip is roll embossed to create a plurality of substantially parallel substantially trapezoidal shaped ribs 14.

[0026] A second roll embossing step is repeated at a different helix angle α. The trapezoidal ribs 14 are deformed, and a plurality of microgrooves 16 and cavities 24 are formed. The second roll embossing step is carefully controlled to create cavities 24 and branched cavities of the preferred geometry.

[0027] Additional rollers may be used by repeating the first roll embossing step to increase the density of cavities, and therefore the heat transfer performance. After performing the roll embossing steps, the copper strip is rolled to create the heat transfer tube 10.

[0028] There are several advantages to utilizing a heat transfer tube 10 with a plurality of cavities 24. For one, the cavities 24 promote nucleate boiling and flow turbulence and enhances the heat transfer performance of the heat transfer tube 10. By increasing the surface area within the tube 10, the amount of surface exposed to fluid is increased, promoting turbulence

[0029] The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specially described. For that reason the following claims should be studied to determine the true scope and content of this invention. 

What is claimed is:
 1. A heat transfer tube comprising: a tubular member having an interior surface, an interior diameter D, and a longitudinal axis; a plurality of substantially parallel ribs formed on said interior surface having a height h₂; and a plurality of cavities formed on said interior surface extending at an angle from said plurality of substantially parallel ribs, each of said plurality of cavities having a cavity depth less than 0.75 h₂.
 2. The heat transfer tube as recited in claim 1 wherein said plurality of substantially parallel ribs are substantially trapezoidal.
 3. The heat transfer tube as recited in claim 1 wherein each of said plurality of cavities are substantially V-shaped.
 4. The heat transfer tube as recited in claim 1 wherein each of said plurality of cavities has a cavity opening less than 0.005 of an inch.
 5. The heat transfer tube as recited in claim 1 wherein each of said plurality of cavities has a cavity depth less than 0.4 h₂.
 6. The heat transfer tube as recited in claim 1 wherein the ratio of said height h₂ of each of said ribs to said interior diameter D of said tubular member ranges from 0.01 to 0.05.
 7. The heat transfer tube as recited in claim 1 wherein the ratio of said height h₂ of each of said ribs to said interior diameter D of said tubular member ranges from 0.015 to 0.03.
 8. The heat transfer tube as recited in claim 1 wherein said plurality of cavities formed in said interior surface extend at an angle from said longitudinal axis of said tubular member ranging from 0 to 45 degrees.
 9. The heat transfer tube as recited in claim 1 wherein said tubular member further includes a circumference and a number of said plurality of deformed ribs per unit length of said circumference ranges between 20 and
 100. 10. The heat transfer tube as recited in claim 1 wherein each of said plurality of ribs has a base width ranging from 0.005 to 0.01 inch and an apex angle ranging from 0 to 60 degrees.
 11. A heat exchanger comprising at least one heat transfer tube having an interior surface, a plurality of substantially parallel ribs formed on said interior surface having a height h₂, and a plurality of cavities formed on said interior surface extending at an angle from said plurality of substantially parallel ribs, each of said plurality of cavities having a cavity depth less than 0.75 h₂.
 12. The heat exchanger as recited in claim 11 wherein said heat exchanger is an evaporator.
 13. The heat exchanger as recited in claim 11 wherein said heat exchanger is a condenser.
 14. A method for making a heat transfer tube comprising: roll embossing a metal strip to form a plurality of substantially parallel ribs formed on said interior surface having a height h₂; re-roll embossing said metal strip to deform said plurality of ribs in said interior surface to form a plurality of cavities extending at an angle from a longitudinal axis of said tubular member plurality of cavities having a cavity depth less than 0.75 h₂. forming said metal strip into a tubular member having an interior surface, an interior diameter D, and said longitudinal axis.
 15. The method as recited in claim 14 wherein the step of roll embossing said metal strip includes forming a plurality of substantially parallel ribs having a substantially trapezoidal shape.
 16. The method as recited in claim 14 wherein the step of re-roll embossing said metal strip includes deforming said plurality of ribs to form a plurality of substantially V-shaped cavities.
 17. The method as recited in claim 14 wherein the step of re-roll embossing said metal strip is rolled at an angle from said longitudinal axis of said tubular member ranging from 0 to 45 degrees.
 18. The method as recited in claim 14 wherein the step of re-roll embossing said metal strip includes forming between 20 and 100 of said plurality of deformed ribs per a unit length of a circumference of said heat transfer tube.
 19. The method as recited in claim 14 wherein the ratio of said height h₂ of each of said ribs to said interior diameter D of said tubular member ranges from 0.01 to 0.05.
 20. The method as recited in claim 14 wherein each of said plurality of ribs has a base width ranging from 0.005 to 0.01 inch and an apex angle ranging from 0 to 60 degrees. 